It is common practice in the glass art to stack glass bodies, particularly flat sheet glass, for packaging, shipping and/or storage. It is also well known to protect glass articles, such as glass sheets, from surface damage by applying an interleaving material between the otherwise contacting glass surfaces. Such diverse materials as wood flour, treated papers, organic polymer particles and various salts have been suggested to avoid either surface marring, staining, or both.
These protective measures have been designed for use in ambient temperature applications. While satisfactory under such conditions, they are generally ineffective for elevated temperature applications. Thus, many materials, particularly those of organic nature, are unstable at elevated temperatures. Previously proposed inorganic materials tend to mar a glass surface at temperatures required for certain thermal processing operations.
Recently, a particular need has arisen in connection with thermally processing thin glass sheets to achieve compaction of the glass. Compaction involves reheating a glass body to a temperature below the glass softening point, but above the maximum temperature reached in a subsequent processing step. This achieves structural rearrangement and dimensional relaxation in the glass prior to, rather than during, the subsequent processing. Preliminary compaction is imperative where it is necessary to maintain precise alignment and/or flatness in a glass body during subsequent processing, as in the manufacture of flat panel display devices.
It is economically attractive to compact glass sheets in stacks. However, this necessitates interleaving, or separating, adjacent sheets to avoid sticking. At the same time, it is necessary to maintain the sheets extremely flat, and with an optical-quality surface finish.